Combustion supervision system

ABSTRACT

A combustion supervision system for use with a fuel burner includes two time delay devices, each of which provides a time delay as a function of current flow through the device. The first time delay device has a shorter time interval than the second time delay device. The system also includes circuitry for energizing the first and second time delay devices concurrently, circuitry for initiating an ignition sequence at the end of the timing interval provided by the first timing device, circuitry for operating a lockout device at the end of the timing interval of the second device, and circuitry responsive to the sensing of flame by a flame sensor for interrupting the timing cycle of the second timing device.

United States Patent [191 Cade [4 June 11, 1974 Primary Examiner-Edward G. Favors [5 7] ABSTRACT A combustion supervision system for use with a fuel burner includes two time delay devices, each of which provides a time delay as a function of current flow through the device. The first time delay device has a shorter time interval than the second time delay device. The system also includes circuitry for energizing the first and second time delay devices concurrently, circuitry for initiating an ignition sequence at the end of the timing interval provided by the first timing device, circuitry for operating a lockout device at the end of the timing interval of the second device, and circuitry responsive to the sensing of flame by a flame sensor for interrupting the timing cycle of the second timing device.

8 Claims, 1 Drawing Figure COMBUSTION SUPERVISION SYSTEM [75] Inventor: Phillip J. Cade, Winchester, Mass.

[73] Assignee: Electronics Corporation of America, Cambridge, Mass.

[22] Filed: Apr. 9, 1973 [2i] Appl. No.: 349,208

[52] US. Cl. 431/78, 43l/79 [51] Int. Cl. F23n 5/08 [58] Field of Search 431/79, 71, 18, 24, 73, 431/74, 78

[56] References Cited UNITED STATES PATENTS 3,171,470 3/1965 Mudd 43l/73 3,306,339 2/l967 Barton et al. 43l/73 3o /M lO |4 BQ-Z 2s Hi i 36 32 58 7 //0 VAC 804 60-l 60-3 WWW PATENTEMM 1 m4 NMNWEN kNN J is N ON COMBUSTION SUPERVISION SYSTEM SUMMARY OF THE INVENTION This invention relates to burner control apparatus and more particularly to burner control apparatus of the combustion supervision type that include circuitry for limiting the trial for ignition interval.

The functions of a combustion supervision system include the automatic ignition of the burner at the beginning of a heating period, the monitoring of the flame, and the shutting down of the burner at the end of the heating period or as a result of abnormal operation. In an illustrative burner cycle, a request for heat is signalled by the closing of contacts of a thermostat or similar control. In response to that signal, a blower is switched on, creating a flow of air through the combustion chamber to purge or clean that chamber of accumulated vapors.- After this purge period, an igniter is energized and a pilot valve is opened to establish pilot flame and the existence of this pilot flame is sensed. Upon sensing of the pilot flame, the main fuel valve is opened and the resulting main flame is monitored by the flame sensor. When the signal requesting heat terminates, the system shuts down the burner. Should abnormal operation occur, for example due to failure of the main flame, the burner is shut down in lockout condition, Typically, a warning signal is generated and a lockout device is operated, the lockout device requiring manual intervention (via a reset switch or pushbutton) before another starting sequence can be initiated.

In such burner systems, the interval in which the ignition system is operated is of limited duration, this interval being termed the trial for ignition period. If flame is not sensed during the trial for ignition interval, the burner is shut down in lockout condition. Frequently, this interval should be only a few seconds in duration while lockout cycles due to other abnormal operation may be of longer duration.

It is an object of this invention to provide an improved combustion control system which provides a timing cycle of short duration.

Another object of this invention is to provide a novel and improved combustion control system that provides a short trial for ignition interval in a simple, reliable and economical circuit arrangement.

In accordance with the invention there is provided a combustion supervision system for use with a fuel burner that includes two time delay devices, each of which provides a time delay as a function of current flow through the device, the first time delay device having a shorter time interval than the second time delay device. The system also includes circuitry for energizing the first and second time delay devices concurrently, circuitry for initiating an ignition sequence at the end of the timing interval provided by the first timing device, circuitry for operating a lockout device at the end of the timing interval of the second device, and circuitry responsive to the sensing of flame by a flame sensor for interrupting the timing cycle of the second timing device.

In preferred embodiments, the second timing device is a main or lockout timer which has an actuator connected in series circuit with the main control so that its operability is verified as a prerequisite for energization of the main control which initiates the ignition sequence, the timing cycle of this main timer being initiated prior to the energization of the main control via a shunt path. In a particular preferred embodiment the first timing device is an auxiliary timer of simple construction, this auxiliary time providing an interval for energizing the flame sensor and flame responsive circuitry prior to energization of the main control. The two timers are energized concurrently, the timing cycle of the auxiliary timer being shorter than that of the main timer and upon completion of the timing cycle of the auxiliary timer, a circuit is completed to energize the main control. Energization of the main control interrupts the shunt path but continues the timing cycle of the main timer until flame is sensed at which time the cycle of the main timer is interrupted. Should flame not be sensed, at the completion of the timing cycle of the main timer, a lockout signal is generated and the system is shut down in lockout.

In a particular embodiment, each timer employs a bimetallic element, the auxiliary timer being a U-shaped bimetal member connected directly in electrical circuit and including a contact member mounted on one leg of the bimetal member in an inexpensive and yet reliable arrangement. The main timer includes a latching arrangement which requires manual reset of the main timer once a lockout signal has been generated.

Other objects, features and advantages of the invention will be seen as the following description of a particular embodiment progresses, in conjunction with the single FIGURE of the drawing which shows, in schematic diagram form, control circuitry incorporating an embodiment of the invention.

DESCRIPTION OF PARTICULAR EMBODIMENT With reference to the drawing, terminals l0, 12 are adapted to be connected to a suitable source of power. Connected to terminal 10 is a suitable switch device 14 such as a thermostat which provides a signal requesting burner operation; and connected across terminals l0, 12 is a set of control devices that includes an alarm control 18, a blower control 20, a main fuel control 22, an ignition control 24, and a pilot fuel control 26. Air flow responsive switch 28 is connected in series between switch 14 and the ignition and fuel controls. Also connected to terminals l0, 12 is a transformer 30 that has a primary winding 32, a 280-volt secondary winding 34, a 280-volt secondary winding 36 that has a tap 38 of 20 volts, an 0.2 volt secondary winding 40 and a 24-volt winding 42 that has a 7-volt tap 44. This transformer 30 has been shown for simplicity of explanation as a single transformer but in a particular embodiment winding 42 is associated with a separate transformer. Connected to high voltage windings 34 and 36 is an ultraviolet flame sensor of the avalanche discharge type and in turn that sensor is connected via inductor 52 to amplifier circuitry that includes transistors 54 and 56 which controls flame relay 60 that has normally open contacts 60-1 and normally closed contacts 60-2 and 60-3. Power for the flame relay circuitry is supplied via a rectifier circuit that includes diode 62 and capacitor 64.

Operating control circuitry includes a control relay 70, connected in bridge rectifier circuit 72, that controls normally open contacts -1 and 70-2 and normally closed contact 70-3. Also connected in the operating control circuitry is a lockout actuator 80, which may be of the type shown in Metcalf US. Pat. No.

3,496,509, and controls normally open contacts 80-1 and normally closed contacts 80-2. This lockout actuator is a bimetallic time delay device which responds to electric current flow therethrough and after the bimetal element has been sufficiently heated by electric current flow, a switch is operated to close alarm control contacts 80-1 and to open lockout contacts 80-2. In this particular embodiment, the time delay imposed by actuator 80 is seconds at nominal line voltage but varies as a function of the voltage, the time delay being greater at low voltages and less at higher voltages.

Connected across winding 40 is actuator 90 of a second time delay device which controls contacts 90-1. This auxiliary actuator also includes a bimetal element through which electric current flows and one member of contacts 90-1 is carried by that bimetal element so that an electrical circuit connection exists between actuator 90 and the flame relay contact 60. In this embodiment this auxiliary timer is a simple U-shaped bimetal element of low thermal mass, one leg of which carries one of contacts 90-1.

Power is normally continuously applied to terminals 10 and 12 and when there is a request for burner operation as signalled by switch 14, a signal is applied through normally closed lockout contacts 80-2 to operate blower 20. When air flow produced by blower is sensed by switch 28, that switch closes and energizes the primary winding 32 of transformer 30. The flame detector 50 is immediately energized; the flame relay amplifier is also similarly energized as it is connected to tap 38 of winding 36; the auxiliary time delay device 90 is energized as it is connected directly across winding 40; and lockout delay actuator 80 is also energized as it is connected in circuit across the upper portion of winding 42 via the normally closed contact 70-3 of the control relay 70. Thus the two time delay devices commence timing cycles simultaneously. When the timing cycle of auxiliary device is completed, the delay in this embodiment being about ten seconds at nominal line voltage, contacts 90-1 close to complete an energizing circuit for the control relay 70 through heater 80, contacts 90-1 and normallyclosed flame relay contacts 60-2. Should there had been a spurious flame signal or other malfunction of the flame relay circuitry such that contacts 60-2 were open, control relay 70 would not be energized but the lockout timer device would continue its timing cycle and at the end of that timing cycle, contacts 80-1 would close energizing alarm 18 and contacts 80-2 would open, de-energizing transformer 32 and shutting down the system in safe condition. Thus this circuit checks both circuitry of heater 80 and the operation of the flame circuitry prior to energization of control relay 70.

Upon energization of control relay 70, contacts 70-1 close establishing a holding circuit for relay coil 70 from tap 44 of secondary winding 42. This holding circuit is independent of the lockout actuator 80. Shunt circuit contacts 70-3 open but element 80 remains energized, however, as a parallel circuit across the upper portion of a winding 42 remains through the closed auxiliary time delay contacts 90-1, flame relay contacts 60-2, and control relay contacts 70-1. This circuit Upon energization of control relay, contacts -2 close, energizing ignition control 24 through normally closed flame relay contacts 60-3 and the pilot fuel control 26. As soon as flame in the combustion chamber is detected by sensor 50, the flame amplifier circuitry responds to that signal produced by that sensor to energize flame relay coil 60. Contacts 60-1 close and contacts 60-2 and 60-3 open. The opening of contacts 60-3 de-energizes the ignition control 24 while the closing of contacts 60-1 energizes the main fuel control 22 so that fuel from the main fuel line flows into the combustion chamber and main flame is established which then is continually supervised by sensor 50. The opening of contacts 60-2 terminate the heating of lockout actuator and the supervised combustion system is now in operating condition, flame relay 60 and control relay 70 normally remaining energized as long as operating control 14 continues to request burner operation.

As soon as operating control 14 terminates the request for operation of the burner, its contacts will open and de-energize the main fuel control 22 and transformer 30, thus de-energizing the flame relay circuitry and the control relay circuitry. With the termination of flow of fuel into the combustion chamber, flame will cease and the apparatus is shut down in anticipation of the next operating cycle.

Thus, the invention provides an economical circuit arrangement in which a main or lockout timing cycle is initiated prior to energization of the control relay and in which a check for the operability of the main timer is required for energization of the control relay. A short trial for ignition interval is provided in a simple circuit arrangement that does not require expensive devices such a motor driven timers.

While this circuitry has been described in connection with a combustion supervision system of the type which uses an ultraviolet sensor, it will be apparent that the invention is applicable to a variety of other combustion control systems, for example those that employ other types of flame sensors such as flame rods or photocells. Further modifications of the circuitry will-be apparent to those skilled in the art. Accordingly, it is not intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. A combustion supervision system for use with a fuel burner comprising a flame sensor, a lockout device, a pilot fuel control, a main fuel control, an ignition control, first and second timing devices, each said timing device providing a time delay as a function of current flow therethrough, said first timing device providing a shorter time interval than said second timing device, circuitry for energizing said first and second timing devices concurrently, circuitry responsive to the end of the timing interval provided by said first timing device for energizing said ignition control and said pilot fuel control for initiating an ignition sequence, circuitry for operating said lockout device at the end of the timing interval provided by said second timing device, and circuitry responsive to the sensing of flame by said flame sensor for interrupting the timing cycle of said second timing device and for de-energizing said ignition control as soon as flame is sensed by said flame sensor.

2. A combustion supervision system for use with a fuel burner comprising a flame sensor, a lockout device, first and second timing devices, each said timing device providing a time delay as a function of current flow therethrough, said first timing device providing a shorter time interval than said second timing device, circuitry for energizing said first and second timing devices concurrently, a main control which initiates an ignition sequence, said second timing device having an actuator connected in series circuit with said main control so that the operability of said actuator is verified as a prerequisite for energization of said main control, circuitry responsive to said first timing device for energizing said main control device to initiate said ignition sequence at the end of the timing interval provided by said first timing device, circuitry for operating said lockout device at the end of the timing interval provided by said second timing device, and circuitry responsive to the sensing of flame by said flame sensor for interrupting the timing cycle of said second timing device.

3. The system as claimed in claim 2 wherein said actuator is energized prior to energization of said main control via a shunt path.

4. The system as claimed in claim 2 wherein said first timing device provides an interval for energizing said flame sensor and said flame responsive circuitry prior to energization of said main control, and circuitry responsive to completion of the timing cycle of said first timing device for energizing said main control.

5. The system as claimed in claim 1 wherein each said timing device includes a bimetallic element.

6. The system as claimed in claim 1 wherein said first timing device comprises a U-shaped bimetal member having a contact member mounted on one leg of said bimetal member that cooperates with a contact member connected directly in electrical circuit with said second timing device, and said second timing device includes a latching arrangement which requires manual intervention for reset of said second timing device.

7. A combustion supervision system for use with fuel burner comprising a flame sensor, a lockout device, first and second timing devices, said first timing device comprising a U-shaped bimetal member having a contact member mounted on one leg of said bimetal member that cooperates with a contact member connected directly in electrical circuit with said second timing device, each said time delay device providing a time delay as a function of current flow therethrough, said first timing device providing a shorter time interval than said second timing device, circuitry for energizing said first and second timing devices concurrently, a main control which initiates an ignition sequence, said second timing device having an actuator connected in series circuit with said main control so that the operability of said actuator is verified as a prerequisite for energization of said main control, circuitry responsive to said first timing device for energizing said main control device to initiate said ignition sequence at the end of the timing interval provided by said first timing device, circuitry for operating said lockout device at the end of the timing interval provided by said second timing device, and circuitry responsive to the sensing of flame by said flame sensor for interrupting the timing cycle of said second timing device.

8. The system as claimed in claim 7 wherein said first timing device provides an interval for energizing said flame sensor and said flame responsive circuitry prior to energization of said main control, said two timing devices are energized simultaneously, the actuator of said second timing device being energized via a path in shunt with said main control, and circuitry responsive to completion of the timing cycle of said first timing device for energizing said main control, energization of said main control interrupting said shunt path but continuing the timing cycle of said second timing device. 

1. A combustion supervision system for use with a fuel burner comprising a flame sensor, a lockout device, a pilot fuel control, a main fuel control, an ignition control, first and second timing devices, each said timing device providing a time delay as a function of current flow therethrough, said first timing device providing a shorter time interval than said second timing device, circuitry for energizing said first and second timing devices concurrently, circuitry responsive to the end of the timing interval provided by said first timing device for energizing said ignition control and said pilot fuel control for initiating an ignition sequence, circuitry for operating said lockout device at the end of the timing interval provided by said second timing device, and circuitry responsive to the sensing of flame by said flame sensor for interrupting the timing cycle of said second timing device and for de-energizing said ignition control as soon as flame is sensed by said flame sensor.
 2. A combustion supervision system for use with a fuel burner comprising a flame sensor, a lockout device, first and second timing devices, each said timing device providing a time delay as a function of current flow therethrough, said first timing device providing a shorter time interval than said second timing device, circuitry for energizing said first and second timing devices concurrently, a main control which initiates an ignition sequence, said second timing device having an actuator connected in series circuit with said main control so that the operability of said actuator is verified as a prerequisite for energization of said main control, circuitry responsive to said first timing device for energizing said main control device to initiate said ignition sequence at the end of the timing interval provided by said first timing device, circuitry for operating said lockout device at the end of the timing interval provided by said second timing device, anD circuitry responsive to the sensing of flame by said flame sensor for interrupting the timing cycle of said second timing device.
 3. The system as claimed in claim 2 wherein said actuator is energized prior to energization of said main control via a shunt path.
 4. The system as claimed in claim 2 wherein said first timing device provides an interval for energizing said flame sensor and said flame responsive circuitry prior to energization of said main control, and circuitry responsive to completion of the timing cycle of said first timing device for energizing said main control.
 5. The system as claimed in claim 1 wherein each said timing device includes a bimetallic element.
 6. The system as claimed in claim 1 wherein said first timing device comprises a U-shaped bimetal member having a contact member mounted on one leg of said bimetal member that cooperates with a contact member connected directly in electrical circuit with said second timing device, and said second timing device includes a latching arrangement which requires manual intervention for reset of said second timing device.
 7. A combustion supervision system for use with fuel burner comprising a flame sensor, a lockout device, first and second timing devices, said first timing device comprising a U-shaped bimetal member having a contact member mounted on one leg of said bimetal member that cooperates with a contact member connected directly in electrical circuit with said second timing device, each said time delay device providing a time delay as a function of current flow therethrough, said first timing device providing a shorter time interval than said second timing device, circuitry for energizing said first and second timing devices concurrently, a main control which initiates an ignition sequence, said second timing device having an actuator connected in series circuit with said main control so that the operability of said actuator is verified as a prerequisite for energization of said main control, circuitry responsive to said first timing device for energizing said main control device to initiate said ignition sequence at the end of the timing interval provided by said first timing device, circuitry for operating said lockout device at the end of the timing interval provided by said second timing device, and circuitry responsive to the sensing of flame by said flame sensor for interrupting the timing cycle of said second timing device.
 8. The system as claimed in claim 7 wherein said first timing device provides an interval for energizing said flame sensor and said flame responsive circuitry prior to energization of said main control, said two timing devices are energized simultaneously, the actuator of said second timing device being energized via a path in shunt with said main control, and circuitry responsive to completion of the timing cycle of said first timing device for energizing said main control, energization of said main control interrupting said shunt path but continuing the timing cycle of said second timing device. 